The moving picture experts group (MPEG) MPEG-2 standard is a compression/decompression standard for interactive video applications. The standard describes an encoding method that results in substantial bandwidth reduction by a subjective lossy compression followed by a lossless compression. The encoded, compressed digital data is subsequently decompressed and decoded in an MPEG-2 compliant decoder.
The MPEG-2 standard specifies a very high compression technique that achieves compression not achievable with intraframe coding alone, while preserving the random access advantages of pure intraframe coding. The combination of frequency domain intraframe encoding and interpolative/predictive interframe encoding of the MPEG-2 standard results in a balance between intraframe encoding and interframe encoding.
The MPEG-2 standard exploits temporal redundancy for motion compensated interpolative and predictive encoding. That is, the assumption is made that "locally" the current picture can be modeled as a translation of the picture at a previous and/or future time. "Locally" implies that the amplitude and direction of the displacement are not the same everywhere in the picture.
The MPEG-2 standard further specifies predictive and interpolative interframe encoding and frequency domain intraframe encoding. It has block based motion compensation for the reduction of temporal redundancy and discrete cosine transform based compression for the reduction of spatial redundancy. Under MPEG-2, motion compensation is achieved by predictive coding, interpolative coding, and variable length coded motion vectors. The information relative to motion is based on a 16.times.16 array of pixels and is transmitted with the spatial information. It is compressed with variable length codes, such as Huffman codes.
Video decoding in accordance with the MPEG-2 standard is described in greater detailed in commonly assigned U.S. Pat. No. 5,576,765, entitled "Video Decoder," which is hereby incorporated herein in its entirety.
One aspect of current video decoding techniques is apparent from the following detailed example. An International Business Machines Corporation MPEGCD1M decoder is designed for a PC platform and its associated applications. This decoder provides a glueless interface to the PCI local bus, with multiple direct memory access ports for high performance data transfer capability. The decoder also provides for the capability to transmit decoded (i.e., decompressed) video image data to system memory or directly to a graphic accelerator's frame buffer. The prior destination is useful for video capture, while the latter destination is employed for display to the PC monitor.
The decompressed video data can have an approximate data rate of 27 MB/sec., and although a 33 MHz PCI bus has a theoretical bandwidth of 132 MB/sec., sufficient bandwidth may not be consistently available to transmit this video data. The PCI local bus does not guarantee that a certain bandwidth will always be available. Obviously, this might be a problem for the transmission of real-time video data without perceptible loss of picture quality.
The present invention addresses the above-noted issue, which can generally be stated as a desire to process decompressed, real-time video data for transmission on a non-real-time medium with minimal loss of perceptible picture quality.